The disclosure refers to turbomachines, and more specifically to axially split turbomachines. Embodiments of the present disclosure specifically refer to sealing arrangements for axially split turbomachines, such as for instance multi-stage centrifugal pumps.
Turbomachines usually comprise an external casing forming a housing wherein a rotor is arranged. The rotor comprises a shaft and one or more impellers keyed on the shaft for rotation therewith. Depending upon the design of the turbomachine, the casing can be vertically split or horizontally split. A horizontally split turbomachine, also named axially split turbomachine, is one wherein the casing is divided into two casing portions along a plane containing the axis of rotation of the rotor. The two casing portions have mutually facing contact surfaces. A sealing arrangement is provided between the opposite contact surfaces. The two casing portions are bolted together by means of bolt-and-nut arrangements. The closure force generates a contact pressure between the contact surfaces and the sealing arrangement.
Sealing arrangements currently used in horizontally split or axially split machine casings include sheets, e.g. made of plastic material, positioned between the contact surfaces of the two casing portions. The bolts, which connect the two casing portions, pre-load the sheet establishing a contact pressure between the surfaces of the sheet and each one of the two contacting surfaces of the opposing casing portions. The contact pressure must be sufficiently high to avoid leakages between the casing portions. A large number of bolts is required, which must be designed and positioned so as to generate a sufficiently high contact pressure between the relatively extensive contacting surfaces.
Sealing sheets are subject to deformation due to the high pressure of the fluid being processed by the turbomachine. The inner edge of the plastic sheet, i.e. the edge facing the rotor housing, is subject to compressive stresses in the plane where the sheet lies. Moreover, the distribution of the contact pressure is uncertain and depends upon many factors. Efficiency of the sealing arrangement is unpredictable and the design process is extremely complex, as the pressure area is dependent upon the strain of the bolts and upon relaxation of the plastic sheet.
There is therefore a need for a more efficient sealing arrangement for axially split turbomachines.